1. Field of the Invention
The invention relates to a hydraulic cylinder and piston having means for preventing rotation of the piston rod within the cylinder, or for preventing rotation of the cylinder about its longitudinal axis relative to the piston rod.
2. Description of the Prior Art
The following U.S. patents have as a general object the prevention of the piston rod from rotating. U.S. Pat. No. 4,736,675, issued Apr. 12, 1988, utilizes a guide rod that extends from a bracket externally attached to the piston rod. U.S. Pat. No. 4,838,146, issued Jun. 13, 1989, uses a complex and fragile device for preventing rotation of the piston rod, the device being externally mounted along the cylinder. U.S. Pat. No. 5,750,952, issued May 12, 1998, uses an internal, off-centered rod parallel to the piston rod to prevent rotation of the piston and piston rod relative to the cylinder. U.S. Pat. No. 4,726,284, issued Feb. 23, 1988, uses a special cylinder that is single acting, one end of the piston defines a slot for receiving the end of the rod having an enlarged cross section. U.S. Pat. No. 5,761,985, issued Jun. 9, 1998, utilizes a square piston rod and has additional complications that would make it difficult to seal the rod and would increase manufacturing cost and maintenance.
The present invention provides a hydraulic cylinder and piston rod unit which finds particular utility for adjusting a surface-piercing marine outdrive. More particularly, the invention provides a double-acting hydraulic cylinder and a piston rod unit in which the cylinder and rod are constrained from relative rotation about their axis. The invention provides a flattened or noncircular in-section end on the unit that is engaged in a slotted member, which in turn is slidably mounted on a housing. The invention prevents relative rotation between the piston rod and cylinder to prevent the attached hoses from becoming twisted and eventually failing. This failure would cause oil spillage and prevent operation of the cylinder and piston rod unit.
More specifically, the unit is able to swivel but is prevented from rotation around its own axis and finds particular utility as a double-acting unit for use in adjusting the surface drive of a marine propeller. The connection between the end of the unit and the boat is waterproof, that is, it is shielded or sealed from the water. The invention can be applied at either end of the cylinder-piston rod unit, depending on which end is attached to the vessel.
The invention is low cost to manufacture and assemble, provides ease of service, and is of robust construction. The parts can be machined with liberal machining tolerances.